linux-kernel - Re: [PATCH] soc: mediatek: pwrap: Zero initialize rdata in pwrap_init

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Date:   Thu, 7 Mar 2019 16:18:33 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-mediatek@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] soc: mediatek: pwrap: Zero initialize rdata in pwrap_init_cipher

On Thu, Mar 7, 2019 at 2:57 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> When building with -Wsometimes-uninitialized, Clang warns:
>
> drivers/soc/mediatek/mtk-pmic-wrap.c:1358:6: error: variable 'rdata' is
> used uninitialized whenever '||' condition is true
> [-Werror,-Wsometimes-uninitialized]
>
> If pwrap_write returns non-zero, pwrap_read will not be called to
> initialize rdata, meaning that we will use some random uninitialized
> stack value in our print statement. Zero initialize rdata in case this
> happens.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/401
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>
> I don't know if this is better or to just restructure the if statement
> below (I'm not an expert in this code so I'll leave that up to the
> maintainers to decide).

No, I the way you have it here is most correct.  That condition writes
a value somewhere, reads it back, then compares it.  The write or read
could fail.  Better to just initialize rdata in case the write fails.
Thanks for the patch.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

>
>  drivers/soc/mediatek/mtk-pmic-wrap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/soc/mediatek/mtk-pmic-wrap.c b/drivers/soc/mediatek/mtk-pmic-wrap.c
> index 8236a6c87e19..2f632e8790f7 100644
> --- a/drivers/soc/mediatek/mtk-pmic-wrap.c
> +++ b/drivers/soc/mediatek/mtk-pmic-wrap.c
> @@ -1281,7 +1281,7 @@ static bool pwrap_is_pmic_cipher_ready(struct pmic_wrapper *wrp)
>  static int pwrap_init_cipher(struct pmic_wrapper *wrp)
>  {
>         int ret;
> -       u32 rdata;
> +       u32 rdata = 0;
>
>         pwrap_writel(wrp, 0x1, PWRAP_CIPHER_SWRST);
>         pwrap_writel(wrp, 0x0, PWRAP_CIPHER_SWRST);
> --
> 2.21.0
>


-- 
Thanks,
~Nick Desaulniers